1. Field of Invention
The present invention relates to a method for manufacturing a porous ceramic structure. More specifically, the present invention relates to a method for manufacturing a porous ceramic structure wherein a temperature rising rate of a firing environment is controlled at the time of firing a molded article formed from a puddle containing a ceramic material as a main component so as to suppress occurrence of cracks in the fired molded article. The present method can be applied to the production of a variety of porous ceramic structures. Particularly, it is suitable for production of a porous honeycomb structure having a higher porosity in which the increase of the internal temperature of a molded article is quite striking, the increase being caused by the combustion of a pore-forming agent that is concurrently contained in a molded article at the time of firing the molded article.
2. Description of Related Art
A porous ceramic honeycomb structure is widely used as means for collecting and removing particulate substances discharged from a diesel engine and the like. In recent years, with respect to the porous ceramic honeycomb structure, an increase in porosity is in progress in response to such requests as a reduction in pressure loss and an improvement in collection efficiency. Thus, a porous ceramic honeycomb structure having a porosity of 40% or more has been gradually becoming a mainstream.
Heretofore, as a method for manufacturing a porous honeycomb structure, a method comprising the steps of forming a molded article by molding a raw material containing a pore-forming agent, and then drying and firing the molded article is widely practiced. Further, carbon or the like has been mainly used as a pore-forming agent due to its lower generation of combustion heat and the like. However, an increase in the amount of the pore-forming agent to be added or the concurrent use of a pore-forming agent capable of forming a higher porosity, such as a foamable resin, is currently in progress in response to the above requests.
However, it has been found that cracks of unknown causes are formed in an obtained ceramic structure, when a molded article containing an increased amount of pore-forming agent such as carbon, or further containing a foamable resin and the like in response to such a request of higher porosity, is fired in accordance with the same temperature raising program as conventionally used. The occurrence of the cracks is a new problem in production of a high porosity ceramic structure.